From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6E828C433DF for ; Wed, 14 Oct 2020 14:37:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D2C0522227 for ; Wed, 14 Oct 2020 14:37:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="SBAsSRY5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D2C0522227 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; 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charset=us-ascii Content-Disposition: inline In-Reply-To: <20201002172559.4000748-4-guro@fb.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000315, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri 02-10-20 10:25:58, Roman Gushchin wrote: > The lowest bit in page->memcg_data is used to distinguish between > struct memory_cgroup pointer and a pointer to a objcgs array. > All checks and modifications of this bit are open-coded. > > Let's formalize it using page memcg flags, defined in enum > page_memcg_data_flags. > > Additional flags might be added later. > > Signed-off-by: Roman Gushchin > Reviewed-by: Shakeel Butt Acked-by: Michal Hocko > --- > include/linux/memcontrol.h | 32 ++++++++++++++++++++------------ > 1 file changed, 20 insertions(+), 12 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index c7ac0a5b8989..99a4841d658b 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -343,6 +343,15 @@ struct mem_cgroup { > > extern struct mem_cgroup *root_mem_cgroup; > > +enum page_memcg_data_flags { > + /* page->memcg_data is a pointer to an objcgs vector */ > + MEMCG_DATA_OBJCGS = (1UL << 0), > + /* the next bit after the last actual flag */ > + __NR_MEMCG_DATA_FLAGS = (1UL << 1), > +}; > + > +#define MEMCG_DATA_FLAGS_MASK (__NR_MEMCG_DATA_FLAGS - 1) > + > /* > * page_memcg - get the memory cgroup associated with a page > * @page: a pointer to the page struct > @@ -404,13 +413,7 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page) > */ > unsigned long memcg_data = READ_ONCE(page->memcg_data); > > - /* > - * The lowest bit set means that memcg isn't a valid > - * memcg pointer, but a obj_cgroups pointer. > - * In this case the page is shared and doesn't belong > - * to any specific memory cgroup. > - */ > - if (memcg_data & 0x1UL) > + if (memcg_data & MEMCG_DATA_OBJCGS) > return NULL; > > return (struct mem_cgroup *)memcg_data; > @@ -429,7 +432,11 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page) > */ > static inline struct obj_cgroup **page_objcgs(struct page *page) > { > - return (struct obj_cgroup **)(READ_ONCE(page->memcg_data) & ~0x1UL); > + unsigned long memcg_data = READ_ONCE(page->memcg_data); > + > + VM_BUG_ON_PAGE(memcg_data && !(memcg_data & MEMCG_DATA_OBJCGS), page); > + > + return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); > } > > /* > @@ -444,10 +451,10 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page) > { > unsigned long memcg_data = READ_ONCE(page->memcg_data); > > - if (memcg_data && (memcg_data & 0x1UL)) > - return (struct obj_cgroup **)(memcg_data & ~0x1UL); > + if (!memcg_data || !(memcg_data & MEMCG_DATA_OBJCGS)) > + return NULL; > > - return NULL; > + return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); > } > > /* > @@ -460,7 +467,8 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page) > static inline bool set_page_objcgs(struct page *page, > struct obj_cgroup **objcgs) > { > - return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs | 0x1UL); > + return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs | > + MEMCG_DATA_OBJCGS); > } > #else > static inline struct obj_cgroup **page_objcgs(struct page *page) > -- > 2.26.2 -- Michal Hocko SUSE Labs